Nowadays, the power combination systems used in the space field are not suitable for really effectively combining more than 4 individual amplifiers at millimeter frequencies. A consequence of this limitation sometimes results in designing semiconductor components with the emphasis on output power to the detriment of the added power yield and the criticality of the designs.
Moreover, these combinations are sometimes insufficient and limiting for obtaining the output powers of SSPAS, meaning “Solid State Power Amplifiers”, required for meeting the real requirements of the applications.
Power combination systems usually comprise a divider, an amplifier and a combiner making it possible to deliver an amplified output signal from an input signal. These systems usually comprise transitions making it possible to change propagation structures such as from a planar structure to a rectangular waveguide or a coaxial waveguide for example.
Today, the main power combination technologies are divided into a first power combination category called arborescent, a second power combination category called spatial and a third power combination category called radial.
The planar arborescent combination techniques make it possible to effectively combine two or four amplifiers. However, these techniques are not suitable for combining a large number of amplifiers because the increase in the number of combination stages and the lengthening of the link lines between the adders of the combiner result in very significantly degrading the signal through combination losses.
In order to minimize these combination losses, metal waveguides can be used instead of planar propagation lines. In this situation, it is then necessary to add transitions between the combiner and the individual amplifiers in order to propagate the signals between the planar lines of the individual amplifiers and the metal waveguides of the combiner. The addition of these transitions and above all the size of the metal waveguides used results in a considerable space requirement for this type of combiner. It is therefore not suitable for combining a large number of amplifiers.
The arborescent combinations as shown in FIG. 1 usually comprise a divider 1 making it possible to divide an input signal 5 into various amplifying channels 2. The various amplified signals leaving the amplifying channels can be propagated and combined in various binary adder stages in a rectangular waveguide 4, 4′, 4″ from a transition 3. An amplified and combined signal 6 can then be processed downstream.
Spatial combination techniques such as the solution developed in U.S. Pat. No. 5,736,908 are characterized in that the amplification device comprises several amplifying channels, usually in the form of plates, which are superposed. The input signal is spread over the amplifying channels by virtue of the spatial distribution of the energy of the signal and is recombined at the output once it has been amplified according to the same principle. These techniques have several drawbacks.
The first drawback is the result of a combination of many amplifiers with this technique. It is then necessary to add supplementary devices in order to be able to excite and combine all the amplifying channels uniformly. Since these supplementary devices add losses, the combination effectiveness of this type of combiner is degraded.
A second drawback is the difficulty of effectively getting rid of the power dissipated by the various superposed amplifying channels. The consequence of this is that, with this type of combination technique, when many amplifiers are combined, it makes it difficult to comply with the requirements imposed by the space field on the maximum temperatures for joining components with semiconductors, which must not be exceeded.
Finally, one drawback is the relative dependency of the amplifying channels, since a failure occurring in one of the amplifying channels can greatly disrupt the general operation of the amplification device.
Radial combination techniques such as the solutions proposed in U.S. Pat. No. 4,700,145, U.S. Pat. No. 4,641,106 and U.S. Pat. No. 4,931,747 are characterized in that the amplification device comprises several amplifying channels, each being connected to the ends of two radial waveguides, the ends being situated between the divider and the combiner, and the two radial waveguides being superposed. This connection makes it possible to amplify a first signal originating from one of the ports of the first radial waveguide and to re-inject it into one of the ports of the second radial waveguide so that it is recombined with the other signals originating from the other ports of the radial waveguide of the combiner.
These techniques have many advantages, notably the reduced space requirement of the amplification device compared to a combination technique with an arborescent structure with rectangular waveguides. Moreover, another advantage is the possibility of improved control over output power reduction induced by the failure of one or more amplifying channels by improving the isolation between the amplifying channels by virtue of absorbent materials or dissipating means placed at the walls of the radial waveguides.
Moreover, radial amplification devices make it possible to combine several individual amplifiers in a single step. The combination losses are therefore reduced relative to the arborescent combination techniques.
On the other hand, a current limitation of these solutions arises from the fact that there is no simple and effective system for compensating for the phase dispersion of the various combined amplifying channels at the time of recombination of the output signal. This drawback makes it necessary to sort the amplifying channels on the basis of the phase of the transmission coefficient or makes it necessary to add variable phase shifters on the amplifying channels in order to compensate for the phase dispersion of the amplifying channels. The latter solution is complex to apply, cumbersome, introduces new losses and optionally consumes additional power.